Update compose Redis

We want to run Redis in CI rather than rely on the fake redis gem.

We also want the major version of Redis to match that in production (7)
locally and in CI.

backing-services-docker-compose.yml

@@ -9,7 +9,7 @@ services:
     volumes:
       - db_data:/var/lib/postgresql/data
   redis:
-    image: redis:4
+    image: redis:7
     ports:
       - "6379:6379"
     volumes:

docker-compose.ci.yml

@@ -11,9 +11,20 @@ services:
     environment:
       DATABASE_CLEANER_ALLOW_REMOTE_DATABASE_URL: "true"
       DATABASE_URL: postgres://postgres:password@db:5432/roda_test
+      REDIS_URL: redis://redis:6379
     env_file:
       - .env.test
+    networks:
+      - test-ci
   db:
     image: postgres:13
     environment:
       POSTGRES_PASSWORD: password
+    networks:
+      - test-ci
+  redis:
+    image: redis:7
+    networks:
+      - test-ci
+  networks:
+    test-ci: